http://arxiv.org/abs/2011.12296
We present a statistical model of the selection function of cold neutral gas in high-redshift (z~2.5) absorption systems. The model is based on the canonical two-phase model of the neutral gas in the interstellar medium and contains only one parameter for which we do not have direct observational priors: namely the central pressure (P) of an L halo at z=2.5. Using observations of the fraction of cold gas absorption in strong HI-selected absorbers, we are able to constrain P*. The model simultaneously reproduces the column density distributions of HI and H$2$, and we derive an expected total incidence of cold gas at z~2.5 of $l{CNM} = 12\times 10^{-3}$. Compared to recent measurements of the incidence of CI-selected absorbers (EW${CI\,1560}$ > 0.4 \r{A}), the value of $l{CNM}$ from our model indicates that only ~15% of the total cold gas would lead to strong CI absorption (EW > 0.4 \r{A}). Nevertheless, CI lines are extremely useful probes of the cold gas as they are relatively easy to detect and provide direct constraints on the physical conditions. Lastly, our model self-consistently reproduces the fraction of cold gas absorbers as a function of N(HI).
J. Krogager and P. Noterdaeme
Thu, 26 Nov 20
61/65
Comments: A&A Letter, Accepted for publication, 5 pages (incl. 2 page auxiliary data table)
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